Circuit protective variable ratio transformer system



y 3, 1954 R. SHERMAN 2,683,820

CIRCUIT PROTECTIVE VARIABLE RATIO TRANSFORMER SYSTEM Filed Oct. 20, 1948 3 Sheets-Sheet l 164 36' 32 2 (if V 3 M 34 ((42% 45 INVENTOR. RALPH SHERMAN.

ATTORAEY July 13, 1954 R. SHERMAN 2,683,820

CIRCUIT PROTECTIVE VARIABLE RATIO TRANSFORMER SYSTEM Filed Oct. 20, 1948 F 3 Sheets-Sheet 2 "I" III];

7 32 RALPH SHERMAN.

$538 I ATTOJWEY y 13, 1954 R. SHERMAN 2,683,820

CIRCUIT PROTECTIVE VARIABLE RATIO TRANSFORMER SYSTEM Filed Oct. 20, 1948 3 Sheets-Sheet 3 (LLUH 732 "M MINI T31 mm; mm

v (Q Y W HH 'j iq {ml 4 8 WW I1, hm 4m...

T42 INVENTOR.

741 RA LFH SHERMAN @J JMW .14 TTORZVZ Y Patented July 13, 1954 CIRCUIT PROTECTIVE VARIABLE RATIO TRANSFORMER SYSTEM Ralph Sherman, Warren, Ohio; Alex Sherman and Arnold Sherman, executors of Ralph Sherman, deceased Application October 20, 1948, Serial No. 55,605

10 Claims. 1

This invention relates to means for permanently or intermitt ly supervising, testing, indicating and controlling the con ion of contact between electrically conductive parts which are required to maintain int ate contact between them, and this without interruption of the operation of the devices or installations which these parts be long to.

invention is applicable to contacts between contacting parts of any kind provided they are capable of conducting electrical energy, but it is particularly valuable in application to systems traversed by a working current, i. e. a current doing useful mechanical, electrical or chemical work, and liable to be disturbed or injured by fundamentally imperfect or suddenly or gradually deteriorating contact between two contacting current-carrying parts.

Certain features disclosed herein but not claimed are claimed in my copending application, Serial No. 495,311, filed January 19, 1943, on which Patent No. 2,459,186 issued January 18, 1949, or in my copending application, Serial No. 719,367, filed December 31, 1945, and Serial No. 351,661, filed April 23, 1953. As to all matters common to this application and said application, Serial No. 95,311, this application is a continuation of application Serial No. 495,311.

It is one of the objects of this invention to provide means whereby the operator of an electrical installation is warned of any imperfection or deterioration of contact in the circuit as soon as it arises, thus enabling him to remedy the deiect before it has resulted in injury to the installation or in material loss of energy or processed material.

Instead of leaving it to the operator to remedy the defect, the diminution or the temporary interruption of current feed may in accordance with my invention be e-liected by means of devices which are activated or thrown in automatically whenever the deterioration of contact exceeds a predetermined limit.

Still another object of my invention is to pr0- vide improved voltage transformation and instrument protective apparatus in which voltage output or voltage ratio is varied to limit voltages. A more specific object of the invention is to provide improved variable voltage transformers.

Still another object of the invention is to insure protection of voltage windings of voltageresponsive measuring or protective apparatus by automatic diminution of voltage applied thereto and disconnection of the winding in the event of appearance of excessive voltages in a system to 2 which such voltage measuring or protective apparatus is connected or in which it is installed.

As is well known to those skilled in the art, electrical conditions in contacts or other parts of electrical circuits, and more especially in heavy current circuits, vary in dependency on the influence exerted on them by the media in which they are operating. Th oxygen or the moisture in the air will cause the formation of an oxid layer on a contact surfacef DustQoil or grease may form insulating coatings thereon. Oxidation may also occur through the action of heat. Loosening of mechanical connections may occur through many causes. In all such cases there results a rise of resistance to the passage of current.

According to this invention the variations in this intermediate resistanc 'are rendered visible or audible in indicating or alarm devices, or are utilized to activate switches, permanently connected to the contacting parts to be protected or supervised, while these parts are traversed by the working current. In any case the attendants or operators are thus warned and induced to remedy the defect or, if necessary, to temporarily throttle or cut out the current.

All' variations of the intermediate resistance between contacting surfaces result in corresponding variations of the voltage drop' at'these surfaces. This is particularly true in thecase of high current installations such as are present in electric melting furnaces operating with currents up to and beyond 50,000 amp. Obviously in such cases any unnoticed rise of the intermediate resistance in a contact may cause very considerable injury to the parts and losses of energy and/or metal. Frequently the electrodes are overheated to the extent of becoming incandescent, arcs may form between the electrodes and their holders, the bus bars may be heated to melting temperature, etc. In most cases the defect that is at the root of all this, will not or cannot be detected in time and the installation may be out of working for many hours or even days.

Hitherto no means have been available for preventing with certainty and automatically the damage arisingfrom such causes.

Numerous. devices are on the market for measuring the specific resistance of solid conductors, but these devices are not suitable for the purpose here in view, 1. e. the detection of imperfect'con tact between contacting parts traversed by" a working current. For, in contrast'to the resistance in solid conductors, the intermediate resistance between contacting parts varies owing to circumstances such as set out above and also to the intensity of current. If this resistance is ascertained or measured under current conditions considerably below those of the normal working current, the results may be deceptive. Therefore in these measuring devices, all of which operate with a separate current, frequently as high a current intensity is used as possible, but since they must be portable, the intensity is limited for technical reasons to a few hundred amperes. Obviously now it is impossible, with so low a current, to correctly measure contact resistances in ap paratus, for instance electric melting furnaces, traversed by many thousand amperes. But quite apart from this technical limitation, these devices are only used to measure resistances in a tie-energized equipment. They do not indicate all condition arising during actual operation, when vibrations or temperature influences or some other circumstances may altogether change the resistance at the contacts, sometimes followed by are formation and eventual melting down of contacting parts.

In contrast to these existing methods of resistance measurement, the present invention enables me to test the conditions of contact in the equipment while it is operating and traversed by the working current, I can provide for a continuous testing and measuring and an automatic signalling of contact conditions and variations, and I may also provide means for automatically throttling or cutting out the current. In every case I utilize the circumstance that any deterioration of contact is accomplished by a corresponding change of voltage drop at the contact. where the amperage is subject to considerable variation, I prefer to use a measuring instrument indicating the quotient of the prevailing system current and voltage, for instance a cross-coil instrument, which is known to indicate directly the resistance, for indicating the disturbance.

While as a rule the working current will be used to actuate the indicating instruments, alarms or switches, I may also use a separate current for this purpose without in any way impairing the result, whichwill be the same as that obtained with the aid of the working current, since I employ the separate current while the working current flows.

For instance, if a separate direct current is used in an alternating current system to indicate the condition of contacts in accordance with my invention, the direct current voltage drop arising from the intermediate resistance exactly corresponds to the actual intermediate resistance formed at this moment by the entire working current. Thus the separate direct current used for testing and indicating these variations furnishes the same picture of the conditions of operations, as would be obtained with the aid of the full working current of thousands of amperes. This method may be particularly advantageous whenever it is desired to eliminate the induction effect exerted on the test (measuring) results. In all cases the operator, without being required to take action for this purpose, is continuously furnished full information regarding any deterioration of the contacts during operation and is thus enabled to prevent in time injury to, or destruction of, the equipment.

I will now proceed to describe by way of example some characteristic applications of my invention in order to thereby show that it will be useful in widely different fields of utilization of Lu cases scribed with reference to the drawings should not in any way be considered as limiting the scope of my claims to the individual means or combinations of means nor to the particular uses and applications shown and described. For there exists hardly any form of electrical installation in which my invention could not be applied with advantage.

Throughout the drawings afiixed to this specification and forming a part thereof, similar numerals are intended to designate similar parts. In the drawings:

l is a diagram of an alternating current system comprising an electrical melting furnace with an electrode mounted in a holder, in combination with means according to this invention for continuously supervising, indicating and controlling the variations of contact between these parts during operation, making use of the working current for efiecting this indication and control.

Fig. 2 illustrates the adaptation of my controlling system to lever switches and more particularly to a double-pole direct-current breaker, in which the supervising device also comprises an auxiliary switch, and in which a new type of voltage transformer is utilized which is particularly adapted for use in my control system, serving for transforming voltages normally below one volt in the secondary winding and for keeping the magnetizing current of the primary winding within predetermined limits, while not allowin high voltage to arise in the secondary winding.

Fig. 3 is a diagram of a system comprising a high tension current oil circuit-breaker in combination with a supervising and controlling device which comprises a similar auxiliary switch.

Fig. 4 is a longitudinal sectional view of the core of the transformer shown in Fig. 2.

Figs. 5 and 6 are schematic diagrams of selflimiting voltage transformers which may be em ployed.

Referring to the drawings and first to Fig. 1, this is a diagram of connections of a circuit feeding alternating current of high intensity through the lead l to the electrode holder 2 of the electrode 3 of an electric melting furnace and through it to the body 5 of molten metal. The condition of contact between the electrode and the holder is supervised and controlled continuously, while the furnace is in operation, or while the supply circuit is connected to a useful load, by providing a measuring instrument which may be permanently connected in the circuit and at any time indicates to the operator whether the contact is good or requires improving. To this end two Wire 8 and 9, connected to the holder and the electrode at 6 and respectively, lead to the primary Winding ll of the voltage transformer ill. The potential of the secondary transformer winding i2 is transmitted by wires 53 and MI to the bridge rectifier 22, while on the other side a wire it leads to the contact piece Hill of a small controller Whose normal position is marked by the letter A, where the current from contact piece I41 passes through the contact segment l5, connecting wire It, segment ll, contact piece Hit and wire 2! to the other side of the rectifier 22 and from one side of the rectifier through wires 23, M3, 24 to the voltage coil 25 of the measuring instrument (cross-coil ohmmeter) 25, from the other side through wire I63, contact 2] and wire 28 to the series resistance 29 allowing adjustment to difierent measuring ranges, and from electrical energy. The examples hereinafter de- 75' this resistance through the brush lid and wire 3| to the second .end of the voltage .coil 25 of the measuring instrument.

The electrode 3 is supplied with current through wire E64, the primary winding 33 of :the current transformer 32, whose secondary winding 34 is connected on one side to the rectifier 42 by way of wire 35, amperemeter 36 and wire 4!, while the other winding is connected to the rectifier by the wire 43. From this rectifier the wire 4? leads to one end of the adjustable shunt 48, while a wire 49 connects the rectiher to the brush-5E! .of this shunt, whose ends are connected on'one side through wires 65, 555 to one end of the current coil 53 of the cross-coil instrument, on the other side through wires 51, 52 to the other end of this coil.

Since the cross-coil ohmmeter directly indicates the ratio of potential and current, the resistance can be read directly on its scales. Ad- -justable series resistance 29 and adjustable shunt 48 are provided for the purpose of adapting the instrument to various conditions in different installations. Since this ohmmeter merely indicates the ratio of potential and current, the amperage fed to the furnace is immaterial to the result. As long as the intermediate resistance between the furnace electrode and the holder remains constant, its pointer |6l will remain stationary. Whenever the contact should deteriorate by a loosening of the electrode in the holder or from other causes the pointer will move at once, and if the deterioration of contact reaches a certain limit, the pointer will establish contact "between the terminals 54 and 59 or" a signalling circuit which comprises the current source 58, one terminal of which is directly connected through wire 57 to the relays 56, while the other terminal is connected to the relays through wire 6'0, closed contacts 59, 54 and wire [66. Relays '55 will now close the contact 64 and thereby excite a suitable protective device with the aid of current supplied by the current source 65. For example, as illustrated in Fig. 2, the relay 58 may be connected to control, through the conductors El and 68, a transformer control winding H3 and/or arelay coil 5| 4. An excess voltage which may arise occasionally, is provided for by a switching relay I39 connected in parallel to the voltage coil 2.5 of the cross-coil instrument by a wire l3l leading to the regulating brush .144, the other wire I32 being connected between wires I43 and 23. Any excess voltage in the potential coil of the instrument will cause the relay I38 to open the contact 21. Further means serving as a protection against excess voltage will be described farther below.

While Figure 1 illustrates an electrode and electrode holder of a furnace, I wish it to be understood that this is merely one example out .of the-great number of points of contact in an alternating current installation which can be controlled and protected in the manner here described. As described in my said parent application, Serial No. 495,311, the principle underlying thisinvention may be applied to both alternating current and directcurrent systems.

In contradistinction to ordinary measuring methods, the present invention is not primarily concerned with the actual magnitude of the ohmic resistance of a contact, the main purpose being to letthe operator know when a deterioration has taken place which renders it necessary for him to take preventive action.

Fig. 2 illustrates an adaptationof .my invention to the protection of lever switches. The

6 figure shows a double-pole circuit breaker 511.. The combination of devices, to be described further below, for testing its contacts and for proin the testing wires leading to the potential coil of the measuring instrument, and the relay for actuating the auxiliary switch is connected to the output side of the circuit breaker. Consequently the relay will throw in the auxiliary switch only after the circuit breaker has been closed and the voltage is available at the output side. A system of well-known locking devices provides for the auxiliary switchto be firstopened before the main switch (circuit breaker) is thrown out.

This device can be used in connection with all kinds of switches and for direct and alternating current as explained in my parent application. For simplicity, alternating apparatus is herein illustrated. It is useful more particularly in all cases where the main switches are not readily accessible or hidden to the eye and difficult to be supervised. In the case of lever switches lacking an automatic actuating device and being arranged for manual operation, the auxiliary switch is also actuated manually. It may, for instance, be thrown in by the bridge of the lever switch, after the lever switch has already passed through part of its path. If the lever switch is opened manually, the auxiliary switch will be opened by means of a spring.

In the combination of a circuit breaker and an auxiliary switch of the kind above described, as illustrated in Fig. 2, the current enters through wires 55! and .596. There is a circuit breaker 51-! comprising movable contacts 503 and 508 cooperating with input terminals 502 and '50! respectively and output terminals 504 and 509.

SIB is the contact (normally closed) and SIS is an auxiliary switch (normally open) actuated by the solenoid coil SIB which coil is connected to the output terminal 509 of the circuit breaker. From this terminal the current flows through wire 5| 7 to one end of the solenoid coil 5i 6, while from the other output terminal 504 current passes through wire 5l2, contact 5 l3 and wire .515 to theother end of the solenoidocoil 5l6.

As soon as the circuit breaker reaches its end position, a full network voltage arises between .theterminals504 and and excites thecoilS i6,

causing the auxiliar switch 5ft to establish connection between the wires and 20?. The rod .539 of the solenoid is suspended by means ofa catch 52'! pivoted to this rod at-528 can move upwardly only while being prevented from turning downwardly by the'stop 529. On the solenoid file being actuated, the catch 52'! meetsthe arm 538 pivoted at 53! and after having been turnedupwardly, moves underneath the arm 53!).

Owing to the wires 26"! and 518 having been connected with each other, the potential coil 25 0f the cross-coil instrument 26 is operatively connected with the input and output terminals of one pole of the circuit breaker, the input'terininal by way of wire I8, contact 5|9 and wire 201, the output terminal 534 through wire 205. The two wires 205 and 207 are connected to transformer leads 8 and 9, respectively. The potential coil of the cross-coil instrument is now operatively connected in the circuit, while the current coil 53 (Fig. 1) is operatively connected by means of leads and 43 to the shunt 533 which is connected with the output terminal 503 by wire 505.

If a particularly great deterioration of the circuit breaker contacts should occur, they would at once be cut out by way of wires 5?, 68, the relay coil 5M being energized, leaving contact 513 open and interrupting the circuit of solenoid coil 5H5, whereby the pull spring 526 is enabled to pull the solenoid back and auxiliary switch 5l9 is opened. The connection leading to the crosscoil instrument is the first to be interrupted. At this moment the catch 52'! meets arm 535 and by turning it reassumes its initial position above arm 535. The turning of this arm cause its other end 532 to close the contact 534, thereby closing a circuit, leading to the trip coil 533 of the circuit breaker, as follows: from One pole of the source of current 537 through wire 538 to one end of the trip coil 539 and from the other end of the same source of current through wire 536, arm 532, contact 534, and wire 535 to the other end of the same trip coil. This causes instantaneous opening of the circuit breaker. The spring 533 returns arm 532 and all the other parts into their initial positions.

Thus the purpose of the auxiliary switchto be thrown in after and thrown out before the main switch (circuit breaker) is attained.

If it is desired to throw out the breaker in the normal manner at the end of the working process, the circuit of the relay coil 554 with its wires 61 and 58 is actuated by means of a separate push-button (not shown) to open the contact 5 I 3.

In the same manner as described above, the circuit breaker will in this case be opened also, since a trip coil is actuated.

This combination operates in the same manner with three-phase current. The testing system of Fig. l is used in combination with the auxiliary switch 5| 9 described above.

Whether operating with direct or alternating (three-phase) current, the check-up devices can be used exactly like in Figs. 1 and 2 of my Patent No. 2,459,186, not only for testing, but also for restoring good circuit continuity where contacts have become defective, as explained more in detail in my copending applications Serial Nos.

719,367 and 719,368, now Patent No. 2,528,558, filed December 31, 19%. The tests may also be carried through with separate current during operations as explained with reference to Figs. 3 and 4 of my Patent 2,459,186. Only in the latter case, two auxiliary switches instead of a single auxiliary switch 5l9, will be required, one for throwing in the separate current source, the other the potential coil. The mode of operation however would remain the same as described with reference to Figs. 3 and 4 of my Patent No. 2,459,186, respectively.

Besides breakers operated by means of closing and trip coils, also manually actuated switches can be protected by the new testing devices. In these cases the auxiliary switch can be actuated manually or mechanically, for instance by forcing down an auxiliary switch by the lever switch bridge. The auxiliary switch is forced down only when the lever switch has already moved into a position where the contacts begin to get closed. Before the manually actuated switch is opened, the auxiliary switch must open first.

Fig. 3 illustrates the application of this invention to the protection of circuits comprising high tension oil break switches. Here also an auxiliary switch will be provided which in view of the high tension will best be designed similarly to a high tension oil switch and for the same voltage, however for a lower amperage. This auxiliary high-tension switch is actuated by the auxiliar low-tension switch, whose mode of operation has been described with reference to Fig. 2.

In the system shown in Fig. 3 the high tension enters through the wires Bill, 632, 633 connected to contacts 354, 569 and 639, respectively. The wiring diagram is shown complete for one phase only; it is identical for the other phases.

A voltage transformer 5k! is connected to two breaker terminals of the two phases on the output side of the high tension oil switch by means of the breaker terminal 535, wire 5E3, fuse 6l5, primary winding EH5 of the transformer, fuse fill and wire Sit leading to the second breaker terminal 5i i. The secondary winding SIS of this voltage transformer feeds an auxiliary low voltage switch M9 or the sam design and arrangement as described with reference to Fig, 2, the numerals which denote similar parts in both figures, being the same throughout.

At the moment when the main high tension oil breaker switch is thrown in, the breaker terminals 6%, Eli receive the tension whereby the voltage transformer 5-H: is excited, whose secondary winding 5m feeds the solenoid coil 5H1 exactly as described with reference to Fig. 2. At the same time the auxiliary low voltage switch 5H is closed whereby the wires 62! and 622 are connected and a low tension source 620 is closed which excites a solenoid coil 523, the current flowing from th current source 325 through wire 62 l, auxiliary switch 5l9 and wire 622 to one end of the solenoid coil 623. The other end of the coil is connected through wire 62% to the same current source 6-20.

The coil 523 on being excited attracts the rod 625 which by means of the movable brush 62B connects the input and output contacts 623 and 527 of the auxiliary high tension switch with each other. Only following this connection the drop of potential arising at the contacts of the main oil switch is transmitted to the testing and protecting device through the output contact 6%, wire E35 and high tension fuse 335 to one end of the primary winding 633 of the voltage transformer 632. The input terminal 584 of the main high tension is connected by means of wire 325, one terminal of the auxliary high tension switch 327, brush 628, the second terminal of the high tension switch 523, wire 635 and fuse 63! to the other end of the primary winding 533.

To the secondary winding 635 of the voltage transformer 5-32 are connected the wires l3 and M which correspond in every respect to the wires l3 and 14 in Fig. l and which also feed the voltage to the potential coil of the cross-coil instrument (not shown) exactly as in Fig. 1.

The output wire 55? of the high tension system extends to the primary winding 645 of the current transformer 539. To the secondary winding 542 are connected the wires 35 and 33 which again, as in Fig. 1, lead to the current coil of the cross-coil instrument.

As shown in Fig. 3, whenever the high tension 9. oil switch is thrown in, the: potential and current coils of the cross-coil instrument are thrown in also and their operation is exactly alike to that of the corresponding parts in Fig. l. The operator is thus enabled to obtain at any time during operation a true picture of the actual state of the contacts of the high tension switch. If the current is cut out under high overcharge or under direct short circuit, it is possible to ascertain instantly after switching in again, whether the contact has deteriorated. By reading the instruments the operator is enabled to decide during which opening interval the high tension switch should be dismounted and overhauled.

Here also for every type of oil switches a certain intermediate resistance is ascertained and determined empirically. If by deterioration of the contacts the intermediate resistance of the high tension oil switch should unexpectedly rise very quickly and exceed a predetermined maximum value, then the protective apparatus will release a signal and/or cut out the switch altogether.

Here also, as in Fig. 2, the auxiliary switch (in this instance a high tension switch), is thrown out first, thereby effecting the throwing out of the entire measuring apparatus and the main high-tension oil switch. To this end the signal sender as (see Fig. 1) sends the impulse through Wires 6?, 68, as already explained with reference to Fig. 2, to the releasing coil 55d of the contact l3'. Again the opening of this contact also opens the auxiliary low tension switch 559 inserted between wires 52 land B22 and the current in the closing coil 6223 is interrupted. The auxiliary high-tension switch is thus opened at once.

As explained with reference to when the rod 539 is pulled back, the rotatable closes a circuit 53'! which actuates the trip coil of the main high-tension switch.

Exactly as in the case of low tension, ii": the main high-tension switch shall be thrown out, an additional push button switch (not shown) is first actuated, which sends an impulse through wires 67, 63 to the coil 5H: for the purpose of opening the auxiliary contact 553.

The means here shown and described for lock ing the auxiliary switchcan of course be replaced by any other electrical or mechanical locking devices.

In certain arrangements it may be advisable to provide an interlocking device with time delay action. This delay could amount to a fraction of. second or any necessary longer time. time delay relay could be advisable, for instance, to avoid any interference with or influence on the instrument 28 due to the capacitance or induction effect which may be greater inhigh voltage systems. The delayed switching of the protective device can be accomplished, as mentioned, not only automatically but also by hand.

In some certain cases where no other disturb ing efiect like capacitance or induction action can be feared, by the switching in of the protective device, we have to consider only that the arrangement never connects the instrument before the switch which has to be supervised is completely in. The same safety rule requiresthat the supervised switch is never disconnected before the instrument itself is disconnected.

In Figs. 2 and 4 I have shown the new voltage transformer serving for transforming the low voltages to the secondary winding without allowing any high voltage that may arise, to reach this winding, and serving further. for keeping lit the magnetizing current of the primary winding within predetermined limits.

The transformer here shown has four limbs 18!, 1G2, 103 and 704. Limb [532 carries the primary winding 633 shown in Fig. 3, while limb which has a very small cross sectional area and is very thin, carries the secondary winding 536.

A third limb 103 having a large cross-section is formed with an air gap 161. The fourth limb I'M having a large cross-section is formed with a large air ap lid. A core H0 extending into the gap lid is normally held in a position where it leaves the gap open by the spring llti acting on the plunger H2 in the closing coil H3 which on being excited, attracts the plunger and causes the core to close the gap. With a normal tension or a fraction of 1 volt the entire flux of magnetic lines of force traverses the small limb Till because the large limbs with their air gaps at so low a magnetization density offer a far too great magnetic resistance, and consequently a fairly complete voltage transfer is obtained. The dimensions of the small limb ill! should however be so chosen that already at a tension of a few volts a full magnetic saturation is obtained. I thereby provide that on the secondary side the tension can rise only up to a predetermined value, since the saturation does not allow the lines of force to be increased indefinitely in the small limb. At a predetermined voltage the magnetic circuit of the large limb its is closed artificially by the solenoid coil H3 driving the core HG into the gap H4, This coil is excited by the signalling contact 66 through wires 3?, E8 of the cross coil instrument, and this instrument allows varying of the voltage at which the solenoid is excited. It may for instance be excited at the moment where a great deterioration of the intermediate resistance arises and besides the optical and acoustical signal also means for reducing the current intensity or for throwing out the circuit breakers are actuated.

0n the gap H4 being closed by the core lit, the greatest part of the magnetic lines of force will find a new passage ofiering. a much lower magnetic resistance. I thereby succeed in keeping the magnetizing current of the primary winding 633 within predetermined limits, thereby preventing this Winding from being destroyed it the primary tension rises strongly.

Since the iron or" the small limb Edi is already saturated, the entire increase of the magnetic flux will for the greater part only take place in the limb 104.

According. to the ratio of the cross-sectional areas and the magnetic resistances of the two limbs I. can obtain that almost no further increase of the lines of force occurs in the small limb and no further rise of the secondary induced tension takes places. At the. moment where the magnetic core enters the air gap, the tension may drop on the secondary side. Therefore a relay such as provided for instance in the telephone bell lines will maintain the signal until it is inter rupted manually by the operator.

By correspondingly choosing the ratios of the limbs, practically any ratio of the voltage normally to be tested and the maximum excess voltage on the primary side can be obtained and the secondary voltage can be kept as low as desired.

In the practical operation of the protective device a retardation may occur in the action of the solenoid whereby the tension may rise further before the whole system has been cut out. In

such a case the magnetization of the large limbs 193 and EM will increase and a considerable part of these lines of force pass through the core Hi3. When the tension has risen sufficiently, the magnetic lines of force will increase at this point to such an extent that the core "H is attracted automatically. In this manner the voltage transformer will achieve automatically, although with a little delay, the effect normally to be achieved by the solenoid.

It might even happen that the gap H4 in the large limb 104 is not closed at all. In that case the second large limb 103 will step in and after a predetermined voltage (magnetization) has been reached, the greater part of the magnetic lines of force will start to pass through the air gap 101 of this limb. In this way a similar effect is obtained as by closing the gap in the large limb 104, and in this case as well the secondary winding 636 is not exposed to an unduly high tension.

In exceptional cases the intermediate resistance in a contact may rise momentarily to a very high value, even as high as several thousand ohms, before the main high tension switch is cut out, and then the magnetization current of the primary winding will also rise considerably. By correspondingly calculating the iron conditions, this magnetization current can be so adjusted that the high tension fuse shown at 535 and 53f in Fig. 3 will blow out when a predetermined voltage and herewith also a predetermined magnetization current is exceeded.

Apart from this protection for the measuring devices, they are also protected by the excess voltage cut-out I30 in Fig. 1.

Obviously the core closing the air gap may have the form of a wedge and it may have any desired cross-section (quadrangular, conical, cylindrical, etc.) and it may be as wide as or less wide than, the limb. The two air gaps H4 and might also be provided at a single limb. I may also provide that simultaneously with the closing of gap 1M an air gap is formed in the small limb 11 which for this purpose is made in two parts. when rising, is ofiered a new, artificially produced path of lower magnetic resistance.

Obviously also the number of limbs and the relative arrangement of the limbs to be opened and closed may be varied. Thus another limb with an air gap closed by a magnetic wedge, or another limb with a permanently open gap may be provided. The secondary limb may carry more than one winding, which may serve different purposes. Similar designs may also be used in the current transformers for the protection of the instrument.

The offering of a new path of lower magnetic resistance for the magnetic lines of force by closing an air gap may also be applied with advantage to the measuring instruments themselves in order to render them safe against the action of excess voltages.

For certain purposes, it may be of advantage, to have another form of this safety instrument transformer as shown for instance in the drawing, Fig. 5. This transformer consists of two parts, which represent the legs of the transformer, and which are turnable around the pivot T31. The primary winding 633 is placed in such a way, that the magnetic flux produced by this winding can flow through the upper legs 733 and 134 or through the lower legs 73! and E32. As it is noticeable from the drawing, the legs 133 and 734 are of manyfold smaller cross-sectional In each case the magnetic flux,

area than legs '53! and 732. The reason for it, is again, as explained by Fig. 2 to achieve the complete saturation of the legs 533 and 73% as soon a the Voltage coming to the primary winding 633 rises over certain permissible value.

These legs E33 and 736 are usually kept together by means of a spring 13 5 which is preferably made of nonmagnetic material. The legs I33 and 734 normally abut at a common surface 135. Both these legs are completely saturated as soon as the voltage in the winding 5% rises over certain value which may be detrimental or dangerous to the actuating device fed by secondary winding $353. A part of the magnetic flux starts, in such case, to go over the legs i3! and F32 which possess manyfold greater cross-sectional area than 33 and 534 but which are usu ally separated by a small air gap 5553. Upon a great increase of the voltage coming to the winding 633, the magnetic flux starts to go more and more from the leg T3! over air gap 335 to the leg E32.

With a very great increase of the magnetic flux, the magnetic pulling action of these both legs will be so great, that it will overcome the tension of the spring 736 and the magnetic pulling force at the space of the small legs. The air gap E36 is then closed so that almost the whole magnetic flux is going over the heavy legs '13! and 132, especially as at the same time an air gap opens at 335 between the legs I33 and 13d.

This action of the transformer prevents too high increase of the voltage in the winding 63% if due to any circumstances the voltage which is normally measured exceeds certain predetermined Values, in a similar way as is explained in regard to Fig. 2.

The joint at the point 73'! can be made in different ways. To avoid excessive friction between laminations, the joint can be constructed, for instance, also in the way as it is shown in the Figure 6. As it is shown in this figure, the legs of this instrument transformer do not cross each other. The magnetic joint of both legs is built more similar to a hinge using some kind of rolling movement. The magnetic joint part '14! can be built, for instance, having a form of a part of a cylinder. The opposite part M8 possesses in such case a round surface with slightly greater radius. The ratio of both radius of part 141 and 148 can be chosen in such a way, that the one leg rolls at the magnetic joint smoothly over the other leg and having so very small friction in contrast to the arrangement of 5, where greater friction can arise due to the magnetic pulling force between the laminations of two different legs.

633 represents again the primary winding, 536 is the secondary winding. A spring 345 keeps the legs M3 and M4 close together at the magnetic contact 145.

In every other respect the instrument transformer of Fig. 6 works in similar way as the transformer of Fig. 5.

To achieve better ratio between the saturation points for the small and heavy legs, and achieve advantage in regard to the dimensions of the transformer, steels of difierent permeability may be used. The small legs would be provided then, for instance, with the steel of very low magnetic permeabilit while the heavy legs would be made out of the steel of higher permeability.

To achieve better magnetic conductivity of the smaller legs, such legs can be provided with any endform which provides for bigger or better magnetic contact. This can be done, for instance, by using small extension of the legs which slide over each other, or in any other way.

To achieve further safety in regard of preven ing that the voltage at the secondary winding 636 rises over certain value, an additional winding can be provided at the small magnetic legs which counteract generally the magnetism in these legs a few percent only, for instance 5%, as long as the transformer is fed by the normal voltage. Such an additional winding may be connected, e. g. in series with the primary winding 633 and be so wound on the leg '5 as to oppose the flux from the winding 633. Upon a large increase of voltage at winding 833, the counteraction of the additional winding will start to act very strong against and so further decrease of magnetic flux in the small legs and, therefore, further safety for the circuit fed by winding 636 is achieved.

The described arrangement can, of course, be used not only as the potential instrument transformer, but also as the current transformer.

The same type of transformers can be used for regulating purposes by varying to this purpose the air gaps while in operation.

If, owing to the occurrence of sudden changes of the magnetic held, an excess voltage should arise in the winding, this can be paralyzed by the provision of resistances of the type described in Patent No. 1,322,742, McEachron, Comprising carbon and silicon carbide with a suitable binder, in which the specific resistance is known to drop considerably in proportion as the voltage rises, or by connectin condensers in parallel to imperiled windings.

In the low-tension system it may also prove useful to provide measuring transformers of similar design for the protection of the instruments against excess voltage.

If a protective equipment according to thi invention is used in connection with an alternating current system operating with very high current intensities, for instance in a circuit comprising an electric melting furnace or a high-duty transformer, it may happen that the testing and signalling lines must be located in the vicinity of very strong magnetic fields whereby they will be exposed to a high induction effect.

In order to paralyze his effect, the wires will be arranged as closely together as possible in order to keep the induction effect as uniform as possible. It may, nevertheless, happen that the induction will not be exactl the same in two wires leading to a protective device, and in such a case an additional voltage may be induced in the measuring wires, which may even amount to a multiple of the normally measur d voltage drop. In order to eliminate this induction effect I prefer connecting with. each other the ends of each pair of measuring wires and to connect to their opposite ends leading to the switchboard a sensitive alternating current voltmeter or a moving coil voltmeter with a rectifier with or without a voltage transformer, or some other sufliciently sensitive indicating instruments. If, in a normal test, the two wires show a diiierence of inductive potentials, one of them is reduced or increased in length until its induction potential is equal to that of the other wire and is thus compensated. The indicating instrument is then replaced by the regular testing device.

Obviously the cross-coil instruments shown and described throughout the specification may be replaced by other suitable measuring or indicat- Ill ing instruments, for instance a wattmeter or an amperemeter in combination with, or without, a series resistance.

The examples of applications of this invention in the protection of electrical systems show that this protection can be obtained with the aid of the working current in direct and in alternating current systems. Protection can be afforded to contacts which normally are closed permanently during operation or to contacts, which must be opened frequently in de-energized condition, further to contacts, including all kind of switches, which are opened and closed during operation and under full tension. The invention is further applicable to conductors and to entire parts of a network. The devices to be used for protection may be stationary or portable and of a merely indicating (signalling) or recording type and may be provided with amplifying devices.

I wish it to be understood that I do not desire to be limited to the exact details disclosed in the specification and drawings, for obvious modifications will occur to persons skilled in the art.

I claim:

1. An instrument transformer comprising in combination a pair of magnetic core members pivoted to each other, each core member comprising a bridge portion in which the two members are pivoted, a saturable portion and a high magnetic permeance portion, the two saturable portions having end surfaces adapted to abut for forming a closed magnetic circuit including the bridge portion of the core members, and the high magnetic permeance portions having end. surfaces normally spaced to form an air gap adapted to be diminished in length upon pivoting of the core members about the pivot to open an air gap between the normally abutting end portions of the saturable core portion, a primary winding linking the bridge portion, a secondary winding linking the saturable core portion, and means for resiliently holding the ends of the saturable core portions in abutment.

2. Apparatus as in claim 1 wherein the bridge portion of one core member is formed as a rounded end and a bridge portion of the other core member is formed as a leg having a socket adapted to receive the other end and of slightly greater radius.

3. A variable ratio transformer comprising in combination a magnetic core having a leg carrying a primary winding, a relatively saturable leg carrying a secondary winding and a pair of legs by-passing the saturable leg, each having an air gap, one of said air gaps being variable in length.

4. Apparatus as in claim 3 including means for varying the length of the air gap.

5. Apparatus as in claim 4 having mechanism for resiliently biasing the air gap varying means to the position of maximum air gap.

6. A variable ratio transformer for avoiding excessive secondary voltage comprising a magnetic core with saturable portion, a primary winding linking said core and a secondary winding linking the saturable portion of the core, said core having a leg by-passing the saturable portion of the core having a relatively large crosssection in relation to said saturable portion and including a variable air gap with means for varying the length of the air gap and mechanism for resiliently biasing the air gap varying means to the position of maximum air gap, the saturable portion of the core being interrupted and so constructed as to introduce an air gap increasing in length upon reduction in length of the first-mentioned air gap.

7. Apparatus as specified in claim 3 wherein a movable plunger is provided for shortening the variable air gap and said plunger is provided with an actuating winding for moving the plunger in the direction of diminishing air gap in response to energization of the actuating winding.

8. In an electrical distribution system apparatus responsive to condition of electrical elements thereof, comprising in combination an electro-responsive device having energizing windings and having contacts closed upon energization of the device exceeding a predetermined value, a variable ratio transformer having a primary winding adapted to be connected to an element in said electrical distribution system and having a secondary winding connected to the energizing winding of said electro-responsive device, said transformer having a magnetic core with a common leg carrying said primary winding, a saturable leg carrying the secondary winding and a by-pass leg including an air gap with a movable lunger adapted to shorten the length of such air gap, said plunger having an actuating coil in circuit with the closing contacts of said electro-responsive device, whereby energization of the electro-responsive device exceeding a predetermined value serves to diminish the air gap of said transformer thereby increasing the leakage and diminishing the magnitude of secondary voltage in relation to primary voltage and protecting said electro-responsive device against excessive energization.

9. In an electrical distribution system, apparatus responsive to condition of electrical elements thereof, comprising in combination an electro-responsive device having energizing windings and a variable ratio transformer having a primary winding adapted to be connected to an element in said electrical distribution system and having a secondary winding connected to an energizing winding of said electro-responsive device, said transformer having a magnetic core with a common leg carrying said primary winding, a saturable leg carrying the secondary winding and a by-pass leg including a variable air gap having movable means responsive to energization for diminishing the length of the air gap whereby energization of the electro-responsive device exceeding a predetermined value serves to diminish the air gap of said transformer thereby increasing the leakage and diminishing the magnitude of secondary voltage in relation to primary voltage and protecting said electro-responsive device against excessive energization.

10. In an electrical distribution system, apparatus responsive to current-conductivity condition of an electrical element thereof comprising in combination a resistance-responsive device of the type having voltage terminals, and a transformer of the variable leakage type in which the ratio of secondary voltage to primary voltage diminishes with increase in primary voltage, said transformer having a primary winding adapted to be connected to the electrical element of the electrical distribution system for producing a re sponse to current-conductivity condition thereof, a secondary winding connected to said voltage terminals, and a core having a leg carrying the primary winding, a saturable leg carrying the secondary winding and a leg by-passing the saturable leg having a relatively large crosssection in relation to the saturable leg and including an air gap adapted to be varied in length, the saturable leg being interrupted and so constructed as to introduce an air gap increasing in length upon reduction in length of the first mentioned air gap.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 390,730 Troy June 16, 1908 1,599,570 Lucas Sept. 14, 1926 1,758,875 Montsinger Apr. 29, 1930 1,943,463 Von Ohlson et a1. Jan. 16, 1934 2,133,919 Fries Oct. 18, 1938 2,140,385 Jones Dec. 13, 1938 2,232,715 Matthews Feb. 25, 1941 2,248,070 Fanger July 8, 1941 2,395,881 Klemperer Mar. 5, 1946 2,459,186 Sherman Jan. 18, 1949 

